11 Solid State Non Stoichiometric Defects F centre For Class 12th Jee Iit Neet Other Exam Vikram Hap

In an ideal crystal, the entropy of the constituents at absolute zero temperature (0K) is zero. However, the crystals generally suffer from certain defects also called imperfections They may be both electronic and atomic in nature. The atomic imperfections may be stoichiometric (Schottky and Frenkel defects) or non-stoichiometric (metal excees and metal deficiency defects). In addition to these, there are impurity defects which are caused by the addition of certain impurities of metals and this is known as dopping. The dopping leads to semi conductors which may be either n-type or p-type in nature. Which is the correct statement regarding F-centres ?

In a ideal crystal there nust be regular repeating arrangement of the constuting particles and its entropy must be zero at absolute zero at absolute zero temperature. However, it is impossible to obtain an ideal crystal and it suffers from certain defects called imperfections. In pure crystal these defects arise either due to disorder or dislocation of the movement of the particles even at absolute zero temperature. Such defect increases with rise in temperature. In addition ti this, certain defects arise due to the pressure of some impurities. Such defects not only modify the existing properties of the crystalline solid but also impart certain new characteritics to them. In pure crystal, e.g, silicon or germanium at 0K, the electrons are prsent in fully occupied lowest energy states and are not xpected to conduct any electricity. However at temperature above 0K, some electron leave their bonds and become free to move in the crystal lattice, giving rise to and become free to move in the crystal lattice, giving rise to electrical conductivity. The electron deficient bonds, called holes (+vely charged) and thermally mobile electrons move in opposite direction under the electric field. Stoichiometric ppoint defects include (a) Schottky defects, which arise due to missing of both cations and anions from their lattice sites without disturbing the stoichiometry and (b) Frenked defects, which arise due to misplacement of certian ions in the crystal lattice. The former defect gives rise to no change of density. Another type of defects are non-stoichometry defects where the cetions and anion are not present in the stoichiometry ratio. In metal excess defect, metal ions or positive ions are in excess as compared to anions of non-metals stoichiometrycally. On the other hand in metal deficiency defect, the cations are in lesser proportion than stoichiometric value. Since the crystal is neutral electrically, the balance of charge is maintained by free electrons or extra positive charges. The metal excess defects gives rise to conduction of electricity due to the presence of free electrons. Also crystals having metal excess defects are paramagnetic and coloured due to the presence of electrons in the anion vacancies. Impurity defects arise when some foreign atoms are present at the lattice sites in place of the host atoms or at the vacant interstitial sites. When 15 group elements like P or are doped into Si or Ge, the added impurity atoms occupy the lattice sites forming four covalent bonds with 4 Si/Ge atoms leaving an extra electron free to move. Such a crystal is said to be n-type semi conductor because the conduction of electricity is due to movement of extra unbounded electrons. If doping of a covalent crystal of 14 group elements are caused by addition of small amounts of elements are caused by addition of small amounts of elements of group 13, e.g, Al or Ga with three valence electrons, one covalent bond formed will be electron deficient and acts as a positive hole. The presence of such holes in the crystal leads to electrical conductivity and the the crystal is said to be p-type semiconductor. Lattice defect per 10^(15)NaCl is 1. What is the number of lattice defects in 1 mole of NaCl?

In a ideal crystal there nust be regular repeating arrangement of the constuting particles and its entropy must be zero at absolute zero at absolute zero temperature. However, it is impossible to obtain an ideal crystal and it suffers from certain defects called imperfections. In pure crystal these defects arise either due to disorder or dislocation of the movement of the particles even at absolute zero temperature. Such defect increases with rise in temperature. In addition ti this, certain defects arise due to the pressure of some impurities. Such defects not only modify the existing properties of the crystalline solid but also impart certain new characteritics to them. In pure crystal, e.g, silicon or germanium at 0K, the electrons are prsent in fully occupied lowest energy states and are not xpected to conduct any electricity. However at temperature above 0K, some electron leave their bonds and become free to move in the crystal lattice, giving rise to and become free to move in the crystal lattice, giving rise to electrical conductivity. The electron deficient bonds, called holes (+vely charged) and thermally mobile electrons move in opposite direction under the electric field. Stoichiometric ppoint defects include (a) Schottky defects, which arise due to missing of both cations and anions from their lattice sites without disturbing the stoichiometry and (b) Frenked defects, which arise due to misplacement of certian ions in the crystal lattice. The former defect gives rise to no change of density. Another type of defects are non-stoichometry defects where the cetions and anion are not present in the stoichiometry ratio. In metal excess defect, metal ions or positive ions are in excess as compared to anions of non-metals stoichiometrycally. On the other hand in metal deficiency defect, the cations are in lesser proportion than stoichiometric value. Since the crystal is neutral electrically, the balance of charge is maintained by free electrons or extra positive charges. The metal excess defects gives rise to conduction of electricity due to the presence of free electrons. Also crystals having metal excess defects are paramagnetic and coloured due to the presence of electrons in the anion vacancies. Impurity defects arise when some foreign atoms are present at the lattice sites in place of the host atoms or at the vacant interstitial sites. When 15 group elements like P or are doped into Si or Ge, the added impurity atoms occupy the lattice sites forming four covalent bonds with 4 Si/Ge atoms leaving an extra electron free to move. Such a crystal is said to be n-type semi conductor because the conduction of electricity is due to movement of extra unbounded electrons. If doping of a covalent crystal of 14 group elements are caused by addition of small amounts of elements are caused by addition of small amounts of elements of group 13, e.g, Al or Ga with three valence electrons, one covalent bond formed will be electron deficient and acts as a positive hole. The presence of such holes in the crystal leads to electrical conductivity and the the crystal is said to be p-type semiconductor. The type of semiconduction shown by crystal capable of showing Schottky defect, will be :

In a ideal crystal there nust be regular repeating arrangement of the constuting particles and its entropy must be zero at absolute zero at absolute zero temperature. However, it is impossible to obtain an ideal crystal and it suffers from certain defects called imperfections. In pure crystal these defects arise either due to disorder or dislocation of the movement of the particles even at absolute zero temperature. Such defect increases with rise in temperature. In addition ti this, certain defects arise due to the pressure of some impurities. Such defects not only modify the existing properties of the crystalline solid but also impart certain new characteritics to them. In pure crystal, e.g, silicon or germanium at 0K, the electrons are prsent in fully occupied lowest energy states and are not xpected to conduct any electricity. However at temperature above 0K, some electron leave their bonds and become free to move in the crystal lattice, giving rise to and become free to move in the crystal lattice, giving rise to electrical conductivity. The electron deficient bonds, called holes (+vely charged) and thermally mobile electrons move in opposite direction under the electric field. Stoichiometric ppoint defects include (a) Schottky defects, which arise due to missing of both cations and anions from their lattice sites without disturbing the stoichiometry and (b) Frenked defects, which arise due to misplacement of certian ions in the crystal lattice. The former defect gives rise to no change of density. Another type of defects are non-stoichometry defects where the cetions and anion are not present in the stoichiometry ratio. In metal excess defect, metal ions or positive ions are in excess as compared to anions of non-metals stoichiometrycally. On the other hand in metal deficiency defect, the cations are in lesser proportion than stoichiometric value. Since the crystal is neutral electrically, the balance of charge is maintained by free electrons or extra positive charges. The metal excess defects gives rise to conduction of electricity due to the presence of free electrons. Also crystals having metal excess defects are paramagnetic and coloured due to the presence of electrons in the anion vacancies. Impurity defects arise when some foreign atoms are present at the lattice sites in place of the host atoms or at the vacant interstitial sites. When 15 group elements like P or are doped into Si or Ge, the added impurity atoms occupy the lattice sites forming four covalent bonds with 4 Si/Ge atoms leaving an extra electron free to move. Such a crystal is said to be n-type semi conductor because the conduction of electricity is due to movement of extra unbounded electrons. If doping of a covalent crystal of 14 group elements are caused by addition of small amounts of elements are caused by addition of small amounts of elements of group 13, e.g, Al or Ga with three valence electrons, one covalent bond formed will be electron deficient and acts as a positive hole. The presence of such holes in the crystal leads to electrical conductivity and the the crystal is said to be p-type semiconductor. In the crystal of Fe_(0.93) O, the percentage of Fe(III) will be:

In a ideal crystal there nust be regular repeating arrangement of the constuting particles and its entropy must be zero at absolute zero at absolute zero temperature. However, it is impossible to obtain an ideal crystal and it suffers from certain defects called imperfections. In pure crystal these defects arise either due to disorder or dislocation of the movement of the particles even at absolute zero temperature. Such defect increases with rise in temperature. In addition ti this, certain defects arise due to the pressure of some impurities. Such defects not only modify the existing properties of the crystalline solid but also impart certain new characteritics to them. In pure crystal, e.g, silicon or germanium at 0K, the electrons are prsent in fully occupied lowest energy states and are not xpected to conduct any electricity. However at temperature above 0K, some electron leave their bonds and become free to move in the crystal lattice, giving rise to and become free to move in the crystal lattice, giving rise to electrical conductivity. The electron deficient bonds, called holes (+vely charged) and thermally mobile electrons move in opposite direction under the electric field. Stoichiometric ppoint defects include (a) Schottky defects, which arise due to missing of both cations and anions from their lattice sites without disturbing the stoichiometry and (b) Frenked defects, which arise due to misplacement of certian ions in the crystal lattice. The former defect gives rise to no change of density. Another type of defects are non-stoichometry defects where the cetions and anion are not present in the stoichiometry ratio. In metal excess defect, metal ions or positive ions are in excess as compared to anions of non-metals stoichiometrycally. On the other hand in metal deficiency defect, the cations are in lesser proportion than stoichiometric value. Since the crystal is neutral electrically, the balance of charge is maintained by free electrons or extra positive charges. The metal excess defects gives rise to conduction of electricity due to the presence of free electrons. Also crystals having metal excess defects are paramagnetic and coloured due to the presence of electrons in the anion vacancies. Impurity defects arise when some foreign atoms are present at the lattice sites in place of the host atoms or at the vacant interstitial sites. When 15 group elements like P or are doped into Si or Ge, the added impurity atoms occupy the lattice sites forming four covalent bonds with 4 Si/Ge atoms leaving an extra electron free to move. Such a crystal is said to be n-type semi conductor because the conduction of electricity is due to movement of extra unbounded electrons. If doping of a covalent crystal of 14 group elements are caused by addition of small amounts of elements are caused by addition of small amounts of elements of group 13, e.g, Al or Ga with three valence electrons, one covalent bond formed will be electron deficient and acts as a positive hole. The presence of such holes in the crystal leads to electrical conductivity and the the crystal is said to be p-type semiconductor. Which of the following statements is correct about the conduction of electricity in pure crystal of silicon at room temperature?

When an atom or an ion is missing from its nomal lattice site a lattice vacanecy (Schottky defect) is created. In stoichmeteric ionic crystals, a vacancy of one ion has to be accompanied by the vacancy of the oppositely charge ion in order to maintain electrical neutrality. In a Frenken defect an ion leaves its position in the lattice and occupies an interstitial void. This id the Frenkel defect commonly found along with the Schottky defects and interstitial. In pure alkali halides. Frenked defects are not found since the ions cannot get into the interstitial sites. Frenkel defects are found in silver halides because of the small size of the Ag^(+) ion. Unike Schottky defects, Frenkel defect do not change the density of the solids. in certain ionic solids (e.g., AgBr) both schottky and Frenkel defect occur. The Defects idiscussed above do not disturb the stoichiometery of the crystalline material. there is large variety of non-stoichiometric inorganic solids which contains an excess or deficienty of one of the elements. Such solids showing deviations from the ideal stoichiometric composition from an important group of solids. For example in the vanadium oxide, VO_(x),x can be anywehere between 0.6 and 1.3 there are solids such as difficult to prepare in the soichiometric omposition thus, the ideal composition in compounds such as FeO is difficult to obtain (normally we get a compositiion of Fe(0.95) O but it may range from Fe_(0.93) O to Fe_(0.96)O ). Non-stoichiometric behavious is most commonly found for transition metal compounds through is also known for some lathanoids and actinoids. Zinc oxide loses oxygen reversible at high temperature and turns yellow in colour. the excess metal is accomodated interstitial, giving rise to electrons trapped in the neighbourhood, the enchanced electrical conductivity of the non-stoichiometric ZnO arises from these electrons. Anion vacancies in alkali halides are produced by heating the alkali halid crystals in an atmosphere of the alkali metal vapour. when the metal atoms deposit on the surface they diffuse into the cystal and after ionisation the alkali metal ion occupies cationic vacancy whereas electron occupies anionic vacancy. Electrons trapped i anion vacancies are referred to as F-centers (From Farbe the German word for colouf) that gives rise to interesting colour in alkali halides. Thus, the excess of potassium i KCl makes the crystal appear violet and the excess of lithium in LiCl makes it pink. Which of the following is most appropritate crystal to show Fremkel defect ?